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S_CLIENT(1)			    OpenSSL			   S_CLIENT(1)

       openssl-s_client, s_client - SSL/TLS client program

       openssl s_client	[-help]	[-connect host:port] [-bind host:port] [-proxy
       host:port] [-unix path] [-4] [-6] [-servername name] [-noservername]
       [-verify	depth] [-verify_return_error] [-cert filename] [-certform
       DER|PEM]	[-key filename]	[-keyform DER|PEM] [-cert_chain	filename]
       [-build_chain] [-xkey] [-xcert] [-xchain] [-xchain_build] [-xcertform
       PEM|DER]	[-xkeyform PEM|DER] [-pass arg]	[-CApath directory] [-CAfile
       filename] [-chainCApath directory] [-chainCAfile	filename] [-no-CAfile]
       [-no-CApath] [-requestCAfile filename] [-dane_tlsa_domain domain]
       [-dane_tlsa_rrdata rrdata] [-dane_ee_no_namechecks] [-attime timestamp]
       [-check_ss_sig] [-crl_check] [-crl_check_all] [-explicit_policy]
       [-extended_crl] [-ignore_critical] [-inhibit_any] [-inhibit_map]
       [-no_check_time]	[-partial_chain] [-policy arg] [-policy_check]
       [-policy_print] [-purpose purpose] [-suiteB_128]	[-suiteB_128_only]
       [-suiteB_192] [-trusted_first] [-no_alt_chains] [-use_deltas]
       [-auth_level num] [-nameopt option] [-verify_depth num] [-verify_email
       email] [-verify_hostname	hostname] [-verify_ip ip] [-verify_name	name]
       [-build_chain] [-x509_strict] [-reconnect] [-showcerts] [-debug]	[-msg]
       [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof]	[-no_ign_eof]
       [-psk_identity identity]	[-psk key] [-psk_session file] [-quiet]
       [-ssl3] [-tls1] [-tls1_1] [-tls1_2] [-tls1_3] [-no_ssl3]	[-no_tls1]
       [-no_tls1_1] [-no_tls1_2] [-no_tls1_3] [-dtls] [-dtls1] [-dtls1_2]
       [-sctp] [-sctp_label_bug] [-fallback_scsv] [-async] [-max_send_frag]
       [-split_send_frag] [-max_pipelines] [-read_buf] [-bugs] [-comp]
       [-no_comp] [-allow_no_dhe_kex] [-sigalgs	sigalglist] [-curves
       curvelist] [-cipher cipherlist] [-ciphersuites val] [-serverpref]
       [-starttls protocol] [-xmpphost hostname] [-name	hostname] [-engine id]
       [-tlsextdebug] [-no_ticket] [-sess_out filename]	[-sess_in filename]
       [-rand file...]	[-writerand file] [-serverinfo types] [-status]	[-alpn
       protocols] [-nextprotoneg protocols] [-ct] [-noct] [-ctlogfile]
       [-keylogfile file] [-early_data file] [-enable_pha] [target]

       The s_client command implements a generic SSL/TLS client	which connects
       to a remote host	using SSL/TLS. It is a very useful diagnostic tool for
       SSL servers.

       In addition to the options below	the s_client utility also supports the
       common and client only options documented in the	"Supported Command
       Line Commands" section of the SSL_CONF_cmd(3) manual page.

	   Print out a usage message.

       -connect	host:port
	   This	specifies the host and optional	port to	connect	to. It is
	   possible to select the host and port	using the optional target
	   positional argument instead.	 If neither this nor the target
	   positional argument are specified then an attempt is	made to
	   connect to the local	host on	port 4433.

       -bind host:port]
	   This	specifies the host address and or port to bind as the source
	   for the connection.	For Unix-domain	sockets	the port is ignored
	   and the host	is used	as the source socket address.

       -proxy host:port
	   When	used with the -connect flag, the program uses the host and
	   port	specified with this flag and issues an HTTP CONNECT command to
	   connect to the desired server.

       -unix path
	   Connect over	the specified Unix-domain socket.

       -4  Use IPv4 only.

       -6  Use IPv6 only.

       -servername name
	   Set the TLS SNI (Server Name	Indication) extension in the
	   ClientHello message to the given value.  If -servername is not
	   provided, the TLS SNI extension will	be populated with the name
	   given to -connect if	it follows a DNS name format. If -connect is
	   not provided	either,	the SNI	is set to "localhost".	This is	the
	   default since OpenSSL 1.1.1.

	   Even	though SNI should normally be a	DNS name and not an IP
	   address, if -servername is provided then that name will be sent,
	   regardless of whether it is a DNS name or not.

	   This	option cannot be used in conjunction with -noservername.

	   Suppresses sending of the SNI (Server Name Indication) extension in
	   the ClientHello message. Cannot be used in conjunction with the
	   -servername or <-dane_tlsa_domain> options.

       -cert certname
	   The certificate to use, if one is requested by the server. The
	   default is not to use a certificate.

       -certform format
	   The certificate format to use: DER or PEM. PEM is the default.

       -key keyfile
	   The private key to use. If not specified then the certificate file
	   will	be used.

       -keyform	format
	   The private format to use: DER or PEM. PEM is the default.

	   A file containing trusted certificates to use when attempting to
	   build the client/server certificate chain related to	the
	   certificate specified via the -cert option.

	   Specify whether the application should build	the certificate	chain
	   to be provided to the server.

       -xkey infile, -xcert infile, -xchain
	   Specify an extra certificate, private key and certificate chain.
	   These behave	in the same manner as the -cert, -key and -cert_chain
	   options.  When specified, the callback returning the	first valid
	   chain will be in use	by the client.

	   Specify whether the application should build	the certificate	chain
	   to be provided to the server	for the	extra certificates provided
	   via -xkey infile, -xcert infile, -xchain options.

       -xcertform PEM|DER, -xkeyform PEM|DER
	   Extra certificate and private key format respectively.

       -pass arg
	   the private key password source. For	more information about the
	   format of arg see "Pass Phrase Options" in openssl(1).

       -verify depth
	   The verify depth to use. This specifies the maximum length of the
	   server certificate chain and	turns on server	certificate
	   verification.  Currently the	verify operation continues after
	   errors so all the problems with a certificate chain can be seen. As
	   a side effect the connection	will never fail	due to a server
	   certificate verify failure.

	   Return verification errors instead of continuing. This will
	   typically abort the handshake with a	fatal error.

       -nameopt	option
	   Option which	determines how the subject or issuer names are
	   displayed. The option argument can be a single option or multiple
	   options separated by	commas.	 Alternatively the -nameopt switch may
	   be used more	than once to set multiple options. See the x509(1)
	   manual page for details.

       -CApath directory
	   The directory to use	for server certificate verification. This
	   directory must be in	"hash format", see verify(1) for more
	   information.	These are also used when building the client
	   certificate chain.

       -CAfile file
	   A file containing trusted certificates to use during	server
	   authentication and to use when attempting to	build the client
	   certificate chain.

       -chainCApath directory
	   The directory to use	for building the chain provided	to the server.
	   This	directory must be in "hash format", see	verify(1) for more

       -chainCAfile file
	   A file containing trusted certificates to use when attempting to
	   build the client certificate	chain.

	   Do not load the trusted CA certificates from	the default file

	   Do not load the trusted CA certificates from	the default directory

       -requestCAfile file
	   A file containing a list of certificates whose subject names	will
	   be sent to the server in the	certificate_authorities	extension.
	   Only	supported for TLS 1.3

       -dane_tlsa_domain domain
	   Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
	   TLSA	base domain which becomes the default SNI hint and the primary
	   reference identifier	for hostname checks.  This must	be used	in
	   combination with at least one instance of the -dane_tlsa_rrdata
	   option below.

	   When	DANE authentication succeeds, the diagnostic output will
	   include the lowest (closest to 0) depth at which a TLSA record
	   authenticated a chain certificate.  When that TLSA record is	a "2 1
	   0" trust anchor public key that signed (rather than matched)	the
	   top-most certificate	of the chain, the result is reported as	"TA
	   public key verified".  Otherwise, either the	TLSA record "matched
	   TA certificate" at a	positive depth or else "matched	EE
	   certificate"	at depth 0.

       -dane_tlsa_rrdata rrdata
	   Use one or more times to specify the	RRDATA fields of the DANE TLSA
	   RRset associated with the target service.  The rrdata value is
	   specified in	"presentation form", that is four whitespace separated
	   fields that specify the usage, selector, matching type and
	   associated data, with the last of these encoded in hexadecimal.
	   Optional whitespace is ignored in the associated data field.	 For

	     $ openssl s_client	-brief -starttls smtp \
	       -connect \
	       -dane_tlsa_domain \
	       -dane_tlsa_rrdata "2 1 1
		 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
	       -dane_tlsa_rrdata "2 1 1
		 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
	     Verification: OK
	     Verified peername:
	     DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate	at depth 1

	   This	disables server	name checks when authenticating	via DANE-EE(3)
	   TLSA	records.  For some applications, primarily web browsers, it is
	   not safe to disable name checks due to "unknown key share" attacks,
	   in which a malicious	server can convince a client that a connection
	   to a	victim server is instead a secure connection to	the malicious
	   server.  The	malicious server may then be able to violate cross-
	   origin scripting restrictions.  Thus, despite the text of RFC7671,
	   name	checks are by default enabled for DANE-EE(3) TLSA records, and
	   can be disabled in applications where it is safe to do so.  In
	   particular, SMTP and	XMPP clients should set	this option as SRV and
	   MX records already make it possible for a remote domain to redirect
	   client connections to any server of its choice, and in any case
	   SMTP	and XMPP clients do not	execute	scripts	downloaded from	remote

       -attime,	-check_ss_sig, -crl_check, -crl_check_all, -explicit_policy,
       -extended_crl, -ignore_critical,	-inhibit_any, -inhibit_map,
       -no_alt_chains, -no_check_time, -partial_chain, -policy,	-policy_check,
       -policy_print, -purpose,	-suiteB_128, -suiteB_128_only, -suiteB_192,
       -trusted_first, -use_deltas, -auth_level, -verify_depth,	-verify_email,
       -verify_hostname, -verify_ip, -verify_name, -x509_strict
	   Set various certificate chain validation options. See the verify(1)
	   manual page for details.

	   Reconnects to the same server 5 times using the same	session	ID,
	   this	can be used as a test that session caching is working.

	   Displays the	server certificate list	as sent	by the server: it only
	   consists of certificates the	server has sent	(in the	order the
	   server has sent them). It is	not a verified chain.

	   Print session information when the program exits. This will always
	   attempt to print out	information even if the	connection fails.
	   Normally information	will only be printed out once if the
	   connection succeeds.	This option is useful because the cipher in
	   use may be renegotiated or the connection may fail because a	client
	   certificate is required or is requested only	after an attempt is
	   made	to access a certain URL. Note: the output produced by this
	   option is not always	accurate because a connection might never have
	   been	established.

	   Prints out the SSL session states.

	   Print extensive debugging information including a hex dump of all

	   Show	all protocol messages with hex dump.

	   Show	verbose	trace output of	protocol messages. OpenSSL needs to be
	   compiled with enable-ssl-trace for this option to work.

	   File	to send	output of -msg or -trace to, default standard output.

	   Tests nonblocking I/O

	   Turns on nonblocking	I/O

	   This	option translated a line feed from the terminal	into CR+LF as
	   required by some servers.

	   Inhibit shutting down the connection	when end of file is reached in
	   the input.

	   Inhibit printing of session and certificate information.  This
	   implicitly turns on -ign_eof	as well.

	   Shut	down the connection when end of	file is	reached	in the input.
	   Can be used to override the implicit	-ign_eof after -quiet.

       -psk_identity identity
	   Use the PSK identity	identity when using a PSK cipher suite.	 The
	   default value is "Client_identity" (without the quotes).

       -psk key
	   Use the PSK key key when using a PSK	cipher suite. The key is given
	   as a	hexadecimal number without leading 0x, for example -psk
	   1a2b3c4d.  This option must be provided in order to use a PSK

       -psk_session file
	   Use the pem encoded SSL_SESSION data	stored in file as the basis of
	   a PSK.  Note	that this will only work if TLSv1.3 is negotiated.

       -ssl3, -tls1, -tls1_1, -tls1_2, -tls1_3,	-no_ssl3, -no_tls1,
       -no_tls1_1, -no_tls1_2, -no_tls1_3
	   These options require or disable the	use of the specified SSL or
	   TLS protocols.  By default s_client will negotiate the highest
	   mutually supported protocol version.	 When a	specific TLS version
	   is required,	only that version will be offered to and accepted from
	   the server.	Note that not all protocols and	flags may be
	   available, depending	on how OpenSSL was built.

       -dtls, -dtls1, -dtls1_2
	   These options make s_client use DTLS	protocols instead of TLS.
	   With	-dtls, s_client	will negotiate any supported DTLS protocol
	   version, whilst -dtls1 and -dtls1_2 will only support DTLS1.0 and
	   DTLS1.2 respectively.

	   Use SCTP for	the transport protocol instead of UDP in DTLS. Must be
	   used	in conjunction with -dtls, -dtls1 or -dtls1_2. This option is
	   only	available where	OpenSSL	has support for	SCTP enabled.

	   Use the incorrect behaviour of older	OpenSSL	implementations	when
	   computing endpoint-pair shared secrets for DTLS/SCTP. This allows
	   communication with older broken implementations but breaks
	   interoperability with correct implementations. Must be used in
	   conjunction with -sctp. This	option is only available where OpenSSL
	   has support for SCTP	enabled.

	   Send	TLS_FALLBACK_SCSV in the ClientHello.

	   Switch on asynchronous mode.	Cryptographic operations will be
	   performed asynchronously. This will only have an effect if an
	   asynchronous	capable	engine is also used via	the -engine option.
	   For test purposes the dummy async engine (dasync) can be used (if

       -max_send_frag int
	   The maximum size of data fragment to	send.  See
	   SSL_CTX_set_max_send_fragment(3) for	further	information.

       -split_send_frag	int
	   The size used to split data for encrypt pipelines. If more data is
	   written in one go than this value then it will be split into
	   multiple pipelines, up to the maximum number	of pipelines defined
	   by max_pipelines. This only has an effect if	a suitable cipher
	   suite has been negotiated, an engine	that supports pipelining has
	   been	loaded,	and max_pipelines is greater than 1. See
	   SSL_CTX_set_split_send_fragment(3) for further information.

       -max_pipelines int
	   The maximum number of encrypt/decrypt pipelines to be used. This
	   will	only have an effect if an engine has been loaded that supports
	   pipelining (e.g. the	dasync engine) and a suitable cipher suite has
	   been	negotiated. The	default	value is 1.  See
	   SSL_CTX_set_max_pipelines(3)	for further information.

       -read_buf int
	   The default read buffer size	to be used for connections. This will
	   only	have an	effect if the buffer size is larger than the size that
	   would otherwise be used and pipelining is in	use (see
	   SSL_CTX_set_default_read_buffer_len(3) for further information).

	   There are several known bugs	in SSL and TLS implementations.	Adding
	   this	option enables various workarounds.

	   Enables support for SSL/TLS compression.  This option was
	   introduced in OpenSSL 1.1.0.	 TLS compression is not	recommended
	   and is off by default as of OpenSSL 1.1.0.

	   Disables support for	SSL/TLS	compression.  TLS compression is not
	   recommended and is off by default as	of OpenSSL 1.1.0.

	   Only	provide	a brief	summary	of connection parameters instead of
	   the normal verbose output.

       -sigalgs	sigalglist
	   Specifies the list of signature algorithms that are sent by the
	   client.  The	server selects one entry in the	list based on its
	   preferences.	 For example strings, see SSL_CTX_set1_sigalgs(3)

       -curves curvelist
	   Specifies the list of supported curves to be	sent by	the client.
	   The curve is	ultimately selected by the server. For a list of all
	   curves, use:

	       $ openssl ecparam -list_curves

       -cipher cipherlist
	   This	allows the TLSv1.2 and below cipher list sent by the client to
	   be modified.	 This list will	be combined with any TLSv1.3
	   ciphersuites	that have been configured. Although the	server
	   determines which ciphersuite	is used	it should take the first
	   supported cipher in the list	sent by	the client. See	the ciphers
	   command for more information.

       -ciphersuites val
	   This	allows the TLSv1.3 ciphersuites	sent by	the client to be
	   modified. This list will be combined	with any TLSv1.2 and below
	   ciphersuites	that have been configured. Although the	server
	   determines which cipher suite is used it should take	the first
	   supported cipher in the list	sent by	the client. See	the ciphers
	   command for more information. The format for	this list is a simple
	   colon (":") separated list of TLSv1.3 ciphersuite names.

       -starttls protocol
	   Send	the protocol-specific message(s) to switch to TLS for
	   communication.  protocol is a keyword for the intended protocol.
	   Currently, the only supported keywords are "smtp", "pop3", "imap",
	   "ftp", "xmpp", "xmpp-server", "irc",	"postgres", "mysql", "lmtp",
	   "nntp", "sieve" and "ldap".

       -xmpphost hostname
	   This	option,	when used with "-starttls xmpp"	or "-starttls xmpp-
	   server", specifies the host for the "to" attribute of the stream
	   element.  If	this option is not specified, then the host specified
	   with	"-connect" will	be used.

	   This	option is an alias of the -name	option for "xmpp" and "xmpp-

       -name hostname
	   This	option is used to specify hostname information for various
	   protocols used with -starttls option. Currently only	"xmpp",	"xmpp-
	   server", "smtp" and "lmtp" can utilize this -name option.

	   If this option is used with "-starttls xmpp"	or "-starttls xmpp-
	   server", if specifies the host for the "to" attribute of the	stream
	   element. If this option is not specified, then the host specified
	   with	"-connect" will	be used.

	   If this option is used with "-starttls lmtp"	or "-starttls smtp",
	   it specifies	the name to use	in the "LMTP LHLO" or "SMTP EHLO"
	   message, respectively. If this option is not	specified, then
	   "" will be used.

	   Print out a hex dump	of any TLS extensions received from the

	   Disable RFC4507bis session ticket support.

       -sess_out filename
	   Output SSL session to filename.

       -sess_in	sess.pem
	   Load	SSL session from filename. The client will attempt to resume a
	   connection from this	session.

       -engine id
	   Specifying an engine	(by its	unique id string) will cause s_client
	   to attempt to obtain	a functional reference to the specified
	   engine, thus	initialising it	if needed. The engine will then	be set
	   as the default for all available algorithms.

       -rand file...
	   A file or files containing random data used to seed the random
	   number generator.  Multiple files can be specified separated	by an
	   OS-dependent	character.  The	separator is ; for MS-Windows, , for
	   OpenVMS, and	: for all others.

       [-writerand file]
	   Writes random data to the specified file upon exit.	This can be
	   used	with a subsequent -rand	flag.

       -serverinfo types
	   A list of comma-separated TLS Extension Types (numbers between 0
	   and 65535).	Each type will be sent as an empty ClientHello TLS
	   Extension.  The server's response (if any) will be encoded and
	   displayed as	a PEM file.

	   Sends a certificate status request to the server (OCSP stapling).
	   The server response (if any)	is printed out.

       -alpn protocols,	-nextprotoneg protocols
	   These flags enable the Enable the Application-Layer Protocol
	   Negotiation or Next Protocol	Negotiation (NPN) extension,
	   respectively. ALPN is the IETF standard and replaces	NPN.  The
	   protocols list is a comma-separated list of protocol	names that the
	   client should advertise support for.	The list should	contain	the
	   most	desirable protocols first.  Protocol names are printable ASCII
	   strings, for	example	"http/1.1" or "spdy/3".	 An empty list of
	   protocols is	treated	specially and will cause the client to
	   advertise support for the TLS extension but disconnect just after
	   receiving ServerHello with a	list of	server supported protocols.
	   The flag -nextprotoneg cannot be specified if -tls1_3 is used.

       -ct, -noct
	   Use one of these two	options	to control whether Certificate
	   Transparency	(CT) is	enabled	(-ct) or disabled (-noct).  If CT is
	   enabled, signed certificate timestamps (SCTs) will be requested
	   from	the server and reported	at handshake completion.

	   Enabling CT also enables OCSP stapling, as this is one possible
	   delivery method for SCTs.

	   A file containing a list of known Certificate Transparency logs.
	   See SSL_CTX_set_ctlog_list_file(3) for the expected file format.

       -keylogfile file
	   Appends TLS secrets to the specified	keylog file such that external
	   programs (like Wireshark) can decrypt TLS connections.

       -early_data file
	   Reads the contents of the specified file and	attempts to send it as
	   early data to the server. This will only work with resumed sessions
	   that	support	early data and when the	server accepts the early data.

	   For TLSv1.3 only, send the Post-Handshake Authentication extension.
	   This	will happen whether or not a certificate has been provided via

	   Rather than providing -connect, the target hostname and optional
	   port	may be provided	as a single positional argument	after all
	   options. If neither this nor	-connect are provided, falls back to
	   attempting to connect to localhost on port 4433.

       If a connection is established with an SSL server then any data
       received	from the server	is displayed and any key presses will be sent
       to the server. If end of	file is	reached	then the connection will be
       closed down. When used interactively (which means neither -quiet	nor
       -ign_eof	have been given), then certain commands	are also recognized
       which perform special operations. These commands	are a letter which
       must appear at the start	of a line. They	are listed below.

       Q   End the current SSL connection and exit.

       R   Renegotiate the SSL session (TLSv1.2	and below only).

       B   Send	a heartbeat message to the server (DTLS	only)

       k   Send	a key update message to	the server (TLSv1.3 only)

       K   Send	a key update message to	the server and request one back
	   (TLSv1.3 only)

       s_client	can be used to debug SSL servers. To connect to	an SSL HTTP
       server the command:

	openssl	s_client -connect servername:443

       would typically be used (https uses port	443). If the connection
       succeeds	then an	HTTP command can be given such as "GET /" to retrieve
       a web page.

       If the handshake	fails then there are several possible causes, if it is
       nothing obvious like no client certificate then the -bugs, -ssl3,
       -tls1, -no_ssl3,	-no_tls1 options can be	tried in case it is a buggy
       server. In particular you should	play with these	options	before
       submitting a bug	report to an OpenSSL mailing list.

       A frequent problem when attempting to get client	certificates working
       is that a web client complains it has no	certificates or	gives an empty
       list to choose from. This is normally because the server	is not sending
       the clients certificate authority in its	"acceptable CA list" when it
       requests	a certificate. By using	s_client the CA	list can be viewed and
       checked.	However, some servers only request client authentication after
       a specific URL is requested. To obtain the list in this case it is
       necessary to use	the -prexit option and send an HTTP request for	an
       appropriate page.

       If a certificate	is specified on	the command line using the -cert
       option it will not be used unless the server specifically requests a
       client certificate. Therefore, merely including a client	certificate on
       the command line	is no guarantee	that the certificate works.

       If there	are problems verifying a server	certificate then the
       -showcerts option can be	used to	show all the certificates sent by the

       The s_client utility is a test tool and is designed to continue the
       handshake after any certificate verification errors. As a result	it
       will accept any certificate chain (trusted or not) sent by the peer.
       None test applications should not do this as it makes them vulnerable
       to a MITM attack. This behaviour	can be changed by with the
       -verify_return_error option: any	verify errors are then returned
       aborting	the handshake.

       The -bind option	may be useful if the server or a firewall requires
       connections to come from	some particular	address	and or port.

       Because this program has	a lot of options and also because some of the
       techniques used are rather old, the C source of s_client	is rather hard
       to read and not a model of how things should be done.  A	typical	SSL
       client program would be much simpler.

       The -prexit option is a bit of a	hack. We should	really report
       information whenever a session is renegotiated.

       SSL_CONF_cmd(3),	sess_id(1), s_server(1), ciphers(1),
       SSL_CTX_set_max_send_fragment(3), SSL_CTX_set_split_send_fragment(3),

       The -no_alt_chains option was added in OpenSSL 1.1.0.  The -name	option
       was added in OpenSSL 1.1.1.

       Copyright 2000-2021 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at

1.1.1k				  2021-03-25			   S_CLIENT(1)


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